1. Field of the Invention
This invention relates to engines that convert the enthalpy of two phase fluids into rotary motion; specifically to a rotary engine which uses a body force (inertia) and structural shape to sequentially restrict the liquid phase of a two phase fluid to angle dependant potential minimums thereby creating "liquid pistons" which confine both phases. Angle dependant cross sections of the enclosing volume allow the volume between pistons to increase with rotation. The resulting differential surface pressure on the rotor surfaces generates torque, rotating the cylinder permitting the performance of external work.
2. Description of Prior Art
Their inherent power density and efficiency have allowed the turbine, in various forms, to dominate large scale power generation applications. Except for trains, steam and gas turbine versions dominate large vehicle propulsion. However, the turbine is very sensitive to solid, even liquid drop contamination and unsuitable for mixed phase fluids. The LAWRENCE LIVERMORE LABORATORY (LLL) terminated their DOE funded program to develop a total flow replacement engine or a total flow turbine compatible with geothermal fluids after an extensive multi-year program. Geothermal applications now either flash the fluid to steam or use heat exchangers despite the resulting much lower efficiency and increased cost.
Several low temperature differential heat sources--salt ponds, ocean water layering, etc.--have been extensively studied but attempts to develop these low density power sources using turbines have failed due principally to the need to use heat exchangers to achieve high quality, pure working fluids. These greatly decrease the efficiency and increase costs.
While the conventional piston engine is less sensitive to solid contaminants than the turbine, a comparatively low power density prevents its use for geothermal applications. further, geothermal sources are essentially saturated liquids and the resulting lubrication problems and possibility of liquid lock further reduce the piston engines' suitability for total flow applications.
The vapor piston engine is not competitive with the turbine and the turbine, while in subsidized use, is not commercially viable in these applications.
Increasing concerns about pollution have resulted in attempts to replace the internal combustion engine with the comparatively pollution free external combustion engine for vehicle propulsion. These attempts initially used conventional vapor piston engines. Limited success resulted in attempts to improve the basic engine and then different architectures. One of the leaders in this research, Lear, alternately used piston engines, a Lysholm screw expander and turbines before terminating his effort.
Low-level efforts to achieve commercial success by modifying the piston engine continue but none are promising.
A rugged, low cost, high power density, total flow engine not requiring the use of heat exchangers would facilitate the use of geothermal fluids and permit the use of many low density heat sources for power generation. One does not exist and the basis for one is not described in the literature or patents.
Efforts to develop commercially useful total flow engines for these applications have led to the invention of several novel architectures. Typical examples of these, most closely related to my invention, are described below.
Schur--in U.S. Pat. No. 3,916,626--describes the most direct representative of one class, the bubble wheel. This engine is a direct inversion of the overshot water wheel in that instead of adding heavy water to one side of a wheel in air they add vapor to the other in liquid.
Schur--U.S. Pat. No. 4,121,420 and Simmons--U.S. Pat. No. 4,233,813--describes versions of this technique in which the vapor is introduced by use of directing bellows.
Brown--U.S. Pat. No. 3,659,416 describes a version of this technique in which the fluid is confined in the rotor but moved from the up to down side by vapor pressure generated by the heating of the liquid on one side of the wheel.
These engines share the very low power density of the water wheel. They do not use the surface pressure of the fluid to generate power, only to move liquid that then falls in a body force field. In these engines an increase of surface pressure beyond that necessary to move the liquid would not increase the power output.
In addition Brown's engine as described poses very difficult heat transfer problems as both heating and cooling must take place in the rotor. They can be modified to flow through versions but would still share the power density limitations.
Siegel--U.S. Pat. Nos. 4,041,705 and 4,135,366--describes engines in which the fluid is moved from one side to another of a two chamber container. The variation in level is coupled by use of a float to the power extractor. As stated, the vapor and liquid need not be of the same substance and a very dense liquid can be used. However, even with the densest liquid available, power density would be very low.
Erazo--U.S. Pat. No. 4,130,993--describes an engine in which a rotor, mounting rings, which permanently confine a liquid, is rotated by the flowing liquid. The fluid flows continuously because of a fixed density difference maintained by differential heating.
The use of centrifugal force to replace gravity as the body force greatly increases the possible power achievable by moving the liquid: but, the heat flow problems in the rotor impose very severe power density limitations.
The engines described above do not have the power density required for commercial success. Schur recognized this and moved from free bubbles to a bellows (piston) to create the low density volume. However, a piston is more efficient and achieves a much greater power density when applied directly to the load as in the conventional piston engine. None of the inventions described above are competitive with the conventional piston engine.
Hansen--U.S. Pat. No. 3,688,502--achieves an increased thruput, as compared to the piston engine, in a novel true turbine by allowing the fluid to flow directly through spiral grooves in two disks in contact. The grooves in the input disk decrease in cross section while those in the output disk increase as a function of distance along the spiral. A closely fitting shroud prevents escape of the fluid from the groves. The liquid and its momentum are transferred from the input to output disk. Either the output or both disks can rotate doing work.
The injector nozzles used require preconditioning of geothermal fluids. However, this turbine should be less sensitive to contaminants than conventional forms. This is its only obvious advantage when compared to conventional turbines. It is not obvious that it is as efficient as conventional versions or that it could use two phase fluids efficiently. Its power density would be much less than conventional turbines.
Spankle--U.S. Pat. No. 3,751,673--describes a version of the Lysholm screw expander. He discusses geothermal applications. The Lysholm is a positive displacement engine with the expansion chamber being defined by the intermeshing of the continuous lobes of a male rotor with continuous grooves in a female rotor--both closely fit by a cover which prevents fluid escape. Torque to rotate the rotors is generated by differential surface pressure on the rotor "fins". The differential pressure is maintained by the sequencing of the chambers. Leo--U.S. Pat. No. 4,228,657--describes a regenerative version of this expander and provides a concise discussion of its operating features with extensive references.
The necessary close fitting of the lobe and grooves in the male and female rotors and their slow withdraw from each other as a function of angle severely limits the volumetric efficiency of this engine. In addition, volumetric efficiency is halved by the use of two rotors to define a volume.
Despite its low power density as compared to the turbine, the ruggedness and simplicity of the Lysholm expander has resulted in its wide consideration for geothermal applications. As stated above, it was considered for vehicle propulsion by Lear. This expander approaches commercially viable performance to cost ratios for several applications. However no existing version, and no version described in the literature, provides the performance to cost ratio margin over conventional engines required to achieve commercial exploitation.